背景:母系遗传的共生体可以诱导共生宿主谱系之间的交配前和/或交配后的生殖隔离,和物种形成,通过修改宿主生殖表型。大型类寄生虫黄蜂属Cotesia(Braconidae)包括多种隐蔽物种,每个人都专门寄生一个到几个相关的鳞翅目宿主物种。这里,我们通过几个微生物共生体对来自15个国家的21个科特西亚物种的感染状况进行了表征,作为研究共生体是否可能为这些寄生虫宿主谱系之间的基因流动提供障碍的第一步。
结果:共生微生物Arsenophonus,Cardinium,在Cotesia黄蜂中未检测到小孢子虫和螺旋体。然而,内共生细菌Wolbachia存在于至少8个科特西亚物种中,因此,我们专注于从NCBI筛选额外的DNA提取物和SRA。一些密切相关的Cotesia物种携带相似的Wolbachia菌株,但是大多数Wolbachia菌株显示出系统发育遥远的宿主谱系之间的水平转移模式。
结论:Wolbachia和Cotesia之间缺乏共同系统发育信号表明,共生体和宿主尚未共同进化到会驱动Cotesia宿主谱系之间物种差异的程度。然而,作为Cotesia物种最常见的兼性共生体,Wolbachia仍可能在类寄生虫黄蜂的生物学中起关键作用。它在这种复杂的神秘物种进化中的确切作用仍有待实验研究。
BACKGROUND: Maternally-inherited symbionts can induce pre-mating and/or post-mating reproductive isolation between sympatric host lineages, and speciation, by modifying host reproductive phenotypes. The large parasitoid wasp genus Cotesia (Braconidae) includes a diversity of cryptic species, each specialized in parasitizing one to few related Lepidoptera host species. Here, we characterized the infection status of an assemblage of 21 Cotesia species from 15 countries by several microbial symbionts, as a first step toward investigating whether symbionts may provide a barrier to gene flow between these parasitoid host lineages.
RESULTS: The symbiotic microbes Arsenophonus, Cardinium, Microsporidium and Spiroplasma were not detected in the Cotesia wasps. However, the endosymbiotic bacterium Wolbachia was present in at least eight Cotesia species, and hence we concentrated on it upon screening additional DNA extracts and SRAs from NCBI. Some of the closely related Cotesia species carry similar Wolbachia strains, but most Wolbachia strains showed patterns of horizontal transfer between phylogenetically distant host lineages.
CONCLUSIONS: The lack of co-phylogenetic signal between Wolbachia and Cotesia suggests that the symbiont and hosts have not coevolved to an extent that would drive species divergence between the Cotesia host lineages. However, as the most common facultative symbiont of Cotesia species, Wolbachia may still function as a key-player in the biology of the parasitoid wasps. Its precise role in the evolution of this complex clade of cryptic species remains to be experimentally investigated.